Vapor Barrier?!

[bad_idea]

I am building a 12x18 room in my 30x40 garage. The room has a ceiling at 9' and the building has 12' walls. I plan to insulate the room and heat it while using the room during the winter. One day I might condition the room year round, but that will not be for some time. I plan to insulate and sheet rock the room. I am in eastern NC, it gets plenty humid here. Should I put in a vapor barrier? If so, on which side of the insulation? Thanks all.

 

[CraigStu]

This will be an interesting thread. I can never remember which it is. Do you put the plastic on the cold side or the hot side. But whichever it is this is always my question. Parts of the year your room (or house) will be warmer than it's surroundings and parts of the year it will be colder (if you cool it later on) than it's surroundings. So parts of the year your barrier will be correct and parts it will be incorrect. Do you go by whichever part is longer in your location?

 

[mike93lx]

If you use one, vapor barrier to the warm side. You want to stop moisture from hitting the cold side and condensing.

 

[beemerphile]

In your climate zone you do not want a vapor barrier. A "vapor barrier" is classified in the IRC as a "Class I Vapor Retarder" - think poly film or other impermeable film. You would be fine with a Class III retarder. This is as simple as a coat of latex paint on drywall.

Make sure that the solution you choose is appropriate for your specific climate zone. What is best in one climate zone may not even be code compliant in another. Here is a good synopsis. In your climate zone, there is no requirement for any vapor barrier at all. What is important is the ability of the wall to dry. You are more likely to cause than prevent moisture problems with a vapor barrier in your climate.

 

[billconner]

If you insulated with foam - XPS sheets I'd suggest as much more economical than spray - it would see solve this. It would be preferable if continuous - on studs not inset.

Non foam insulation, I think I'd go with vapor barrier on outside if primarily air conditioning inside.

beemerphile is right. Insulate with cellulose which handles moisture and dries well - and no vapor barrier. Drywall both sides?

 

[bad_idea]

Two of the room's walls are interior and two are exterior. The exterior is OSB with vinyl siding. The interior walls in the room will be drywall, and the walls on the other side will be OSB. I plan to weld and grind in the room, so I want to use 5/8 drywall for the fire retardant values.

I plan to use fiberglass batts in the ceiling cavity - they do not come with any kind of vapor barrier on them. I plan to use fiberglass batts in the walls. The batts in the walls with Kraft paper backing would be easiest to install. Sound like a plan?

 

[billconner]

If you can't get batts for walls w/o the kraft paper, put it to outside/warm side.

I never had problems installing untaxed fiberglass batts in walls. friction holds them quite well.

 

[964haus]

If you use one, vapor barrier to the warm side. You want to stop moisture from hitting the cold side and condensing.

^^ Here in BC, this is what we do.